The diameter of a given bundle of light rays passing through a lens determines the brightness of the image formed. The maximum diameter of this bundle depends on the optical diameter of the lens. By placing plates with holes of various sizes, or a set of metal leaves to form an adjustable hole, in the light path of a lens it is possible to adjust the diameter of this bundle of rays, and hence the intensity of illumination of the image. The device with such a hole is known generally as a diaphragm.
An iris diaphragm is usually formed by a set of thin metal blades mounted on a ring around the lens. Closing the blades inwards makes the hole smaller. Opening the blades makes the hole larger. The greater the number of blades in an iris diaphragm, the more nearly the hole approaches a perfectly circular shape similar to the lens. In a camera or a photographic printer, the iris diaphragm is generally an integral part of the lens/shutter assembly. Iris diaphragms are also used in other optical systems--e.g., on the substage condenser of a microscope.
When cost is a significant factor in the manufacture of an iris diaphragm, such as in an inexpensive camera, it has been suggested that the iris diaphragm be a simple one-piece structure. By way of example, commonly assigned prior art U.S. Pat. No. 3,348,463 issued Oct. 24, 1967 discloses a one-piece iris diaphragm comprising several blades, a drive lever integrally formed with one of the blades, and flexible interconnections between the blades.